This invention is a paper feeding mechanism for preventing more than one sheet of paper from being delivered to a gripper bar and more specifically comprises a first biasing means for pressing the stack against the belt to pull one or more sheets from the stack and a second biasing means for flattening those selected sheets against the belt so that an accurate gap can prevent more than one sheet from going onward toward the gripper bar.
Computer cards are typically placed into a computer in the form of a stack. The card reader then reads each card. A typical mechanism for preventing the feeding of more than one card at a time is described in an IBM Technical Disclosure Bulletin, Vol. 14 No. 8 January 1972, Vernierly Adjustable Throat for Document Card Hoppers by J. R. Reidenbach. A set of rollers drives one or two cards from the bottom of a stack toward a gap defined by an adjustable ramp 12 and a fixed knife 10. The gap is adjusted to allow only one card at a time to pass.
A similar mechanism is described in a U.S. Pat. No. 4,004,795, Hopper Mechanism by Agnew et al. Here the vertically stacked cards are driven downward into a gap defined by a fixed knife 52 and an adjustable ramp 50. Another mechanism is described in U.S. Pat. No. 3,874,652, Apparatus for Feeding Sheet Material from the Bottom of a Stack by Robert A. Bilbrey. A loader plate 45 presses the forward edge of the stack against the moving belt, forcing one or two sheets forward. The adjustable gap between the belt and the gate 85 then allows only one sheet to pass.
A special case arises when the stack to be fed comprises sheets of paper with a forward edge length of 81/2 inches (18.7 cm) rather than a few inches in the case of a computer card. The problem is compounded if the paper is rigid or stiff, as is the case in a system which develops x-ray images. The greater rigidity of the sheet results in a greater likelihood of sheet warping, the longer distances between mechanism elements lead to a greater probability of mechanical misalignments, and together these result in a greater likelihood of paper jams. What is required is a page-sized paper feeder which will feed one sheet of stiff paper at a time while minimizing paper jams.